1. Field of the Invention
The invention relates to a bandgap reference circuit, and more particularly to a high voltage and low quiescent current bandgap reference circuit.
2. Description of the Related Art
Electronic circuits, such as analog to digital converters, linear or switching voltage regulators and so on, often require a reference voltage which is stable and constant despite temperature and power supply variations. A bandgap reference circuit is typically used to provide such a temperature-independent and power-supply-independent reference voltage which is referred to as a bandgap voltage.
FIG. 1 shows a conventional bandgap reference circuit 100. The bandgap reference circuit 100 utilizes a feedback loop to establish an operating point such that an output voltage VREF is generated by a first voltage and a second voltage. The first voltage is related to a multiple of the base to emitter voltage differential (ΔVBE) of a pair of transistors Q1 and Q2 operating at different current densities, and the second voltage is related to the base to emitter voltage VBE of a transistor Q3. In FIG. 1, the transistors Q1, Q2 and Q3 are NPN type bipolar junction transistors. Furthermore, the first voltage ΔVBE is proportional to the absolute temperature (PTAT) and thus has a positive temperature coefficient, and the second voltage VBE has a negative temperature coefficient. Thus, the sum of KΔVBE (where K is a multiple) and the base to emitter voltage VBE produces a voltage that has nearly no temperature dependence and no power-supply dependence.
In general, an analog circuit needs a stable bandgap voltage for proper performance. However, most high voltage analog circuits do not have a temperature-independent and power-supply-independent bandgap voltage. Therefore, providing a high voltage and low quiescent current bandgap reference circuit for a high voltage analog circuit is desired.